Health experts suspect the substance has only recently arrived in New Zealand, and say it is similar to a government-approved substance found in nine herbal highs sold in R18 shops.

The 43-year-old will appear in the Christchurch District Court on Wednesday.

Constable Michael Kneebone said the suspect told police he thought he was putting "speed" (amphetamine) in the drink and did not realise it was in fact a synthetic drug.

It was unknown how much of the drug the 53-year-old consumed, but Kneebone said he collapsed "within a matter of minutes" of drinking the spiked beer.

Restaurant staff went to the man's aid and phoned emergency services.

A month on from the September 29 incident, the man's health was "still not 100 per cent". However, he was expected to make a full recovery, Kneebone said.

National Poisons Centre toxicologist Dr Leo Schep said AB-Pinaca was similar to AB-Fubinaca, which is currently on the Government's list of interim approved products. It is contained in products including Tai High and Illusion Peak.

How dangerous the product was would emerge in time, Schep said.

Dr Paul Gee, Christchurch Hospital emergency specialist, said the number of patients being admitted with symptoms including panic attacks, heart palpitations, intractable vomiting and psychosis after taking synthetic cannabis had not fallen since the Psychoactive Substances Act took effect in August.

In Christchurch, that number was about a dozen a month. Most patients were adults, but some were as young as 12, he said.

Schep and Gee have started testing 20 synthetic cannabis products to establish which, if any, were safe for human consumption.

Psychoactive Substances Regulatory Authority manager Dr Donald Hannah said the authority learnt of AB-Pinaca only last week, after being contacted by police.

No interim approved synthetic cannabis products contained AB-Pinaca. Because it was not an approved substance, it was illegal under the Psychoactive Substances Act, Hannah said.